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A hard disk draws between 7W and 9W when idle, and up to 13W when reading data. Hard disks also generate heat that needs to be dissipated by other electrical components. If you have two or more computers that need access to lots of storage, think about installing a NAS device rather than multiple hard disks.

Running a NAS box on your network 24 hours a day, every day of the year, would cost around £40. This is the equivalent of using a laptop PC for around 40 hours a week, or owning and watching a 32in LCD TV.

Home entertainment

32in LCD TV
(in use/standby) 158W/3W
Typical cost per year £48

Freeview
(in use/standby) 6W/4W
Typical cost per year £4.50

Sky (in use/standby) 20W/5W
Typical cost per year £8.50

Sky+ (in use/standby) 37W/20W
Typical cost per year £24.50

V+ (in use/standby) 28W/28W
Typical cost per year £27

DVD player
(in use/standby) 24W/1W
Typical cost per year £5.50

Big-screen TVs and other home entertainment devices have been singled out as massive power consumers, particularly in standby mode, but the situation isn't as bleak as you might think.

A 42in plasma TV draws 305W when it's running, but this

Screen brightness also plays a big part in a TV screen's power consumption. If you haven't fiddled with your TV's screen settings since the day you bought it, it's worth digging out the manual to see if you can reduce the brightness without adversely affecting image quality. You'll save money that way.

TVs are only one component in a typical home entertainment setup. Most living rooms have a set-top box of some kind. The most frugal of these is a Freeview receiver, drawing just 6W when active and 4W in standby mode. A Sky Digibox is more power-hungry, drawing 20W when active and 4W in standby mode.

With their multiple tuners and spinning hard disks, personal video recorders (PVRs) use more power. Sky+ draws 37W when active, while Virgin Media V+ draws 28W. Since they're designed to be constantly buffering a channel to the hard disk, even when they aren't recording a programme, it's hard to see how a PVR's power consumption can be cut. Sky+ and V+ have a standby mode, but until recently this did little more than cut the output from the SCART socket and change the green power LED to red.

Sky recently issued a software update that puts its Sky+ and Sky+ HD boxes into standby mode between 11pm and 4am if the box isn't used for two hours. Standby mode was changed to turn off the fans and make the hard disk spin down, thereby reducing power consumption to 20W. The box still records shows as required, but Sky claims that putting its 184,000 Sky+ HD boxes and 2,130,000 Sky+ boxes in standby mode for 10 hours a day equates to a saving of 73,613,200kWh over a year. This is enough to light all the homes in Wolverhampton for 12 months.